President Bush has vowed that the United States will remain in Iraq, saying a premature withdrawal would embolden the terrorists.

At a news conference at the White House Wednesday, Mr. Bush acknowledged recent violence in Iraq, including the killing of the brother of Iraq's Sunni Arab vice president, who was shot dead in his home earlier in the week.

The president also dismissed a study published Wednesday that estimated some 655,000 Iraqis have died as a result of the war.

He said he does not consider the report credible, and that the methodology used is "pretty well discredited."

The study in the British journal, The Lancet, says about 600,000 of the 655,000 Iraqis died from violence, mostly gunfire. Researchers also found a small increase in deaths from disease and other causes.

The figure is far higher than other estimates. President Bush estimated in December that about 30,000 people have died as a result of the war.

When asked if he still stood by his estimate, Mr. Bush said he stands by the figure that "a lot" of innocent people have died in the conflict.

Wednesday in Geneva, the top United Nations humanitarian aid official, Jan Egeland, said the violence in Iraq is going unchecked, claiming about 100 lives per day.

The study in The Lancet was conducted by Iraqi and U.S. researchers who interviewed residents of more than 1,800 randomly selected households at 47 sites in Iraq. They compared the mortality rates to pre-war estimates.

In 2004, the same group published an estimate of 100,000 deaths in the first 18 months after the U.S-led invasion of Iraq.